1. Field of the Invention
The present invention relates generally to a vibration sensor for an automotive vehicle which can detect mechanical vibrations generated from an internal combustion engine, such as knocking, and more specifically to a vibration sensor for an automotive vehicle having a piezoelectric vibration element therein mounted in cantilever fashion.
2. Description of the Prior Art
Generally, if strong engine knocking continues for a long time while an internal combustion engine is in operation, the knocking will adversely affect the engine's durability and performance. However, it has also been known that the best engine operating conditions with respect to engine torque characteristics and fuel consumption rate can be obtained when the engine rotates with a weak knocking at a relatively slow engine speed.
Heretofore, various systems have been proposed which can detect engine knocking conditions and regulate the engine spark timing so as to maintain a weak knocking state at all times for improvement in engine torque characteristics and fuel consumption rate.
Engine spark timing control systems of this sort have already been disclosed by U.S. Pat. No. 4,002,155 and No. 4,012,942.
In the systems mentioned above, a vibration sensor is indispensable in order to detect the knocking conditions of an internal combustion engine, that is, to detect the engine vibration accompanied with knocking.
Conventionally, a round-shape piezoelectric vibration element has been used for this vibration sensor. Since a conventional round-shape piezoelectric vibration is fixed to the housing at its periphery, the vibration is susceptible to thermal deformation whenever the temperature changes sharply, thereby resulting in a change in resonant frequency of the vibrator.
Therefore, there has been a need for a vibration sensor for an automotive vehicle which is stable enough despite any abrupt temperature change without changing the resonant frequency of the vibrator.